composed of _seminiferous tubules_,
which are greatly convoluted and likewise branched, the branches being
continuous with those of neighbouring tubules, both within the same
lobule, and (by perforating the fibrous septa) in adjoining lobules. In
the walls of the seminiferous tubules the _spermatozoa_ are formed. The
seminiferous tubules unite to form the efferent ducts (_vasa
efferentia_), about a dozen in number for each testicle; immediately
passing out of the testicle, these efferent ducts make up the
_epididymis_, situated at the upper and back part of the testicle. After
numerous convolutions, these unite at length on each side to form a
single canal, which leaves the epididymis under the name of the _vas
deferens_; this is the excretory duct of the testicle, conveying the
secretion of that organ to the exterior. The vas deferens traverses the
inguinal canal into the abdominal cavity, and therein passes downwards
to the prostatic portion of the urethra (_vide infra_). The anterior
portion only of the _penis_ is visible externally, dependent in front
of the scrotum; the posterior portion is concealed by the scrotum and
the skin of the perineum. The terminal segment of the penis is formed by
the _glans_, which is covered by the _foreskin_ or _prepuce_. This last
is sometimes artificially removed: either on ritual grounds, as, for
instance, among the Jews; or for medical reasons, for example, when the
preputial orifice is greatly constricted. At the anterior extremity of
the glans penis is the orifice of the urethra (_meatus_). The _urethra_
is a canal running through the entire length of the penis, opening by
its proximal extremity into the urinary bladder, and serving for the
passage of the urine from the bladder to the exterior of the body. The
main substance of the penis is composed of three cavernous bodies, the
paired _corpora cavernosa penis_, and the single _corpus spongiosum_, or
_corpus cavernosum urethrae_. These consist of what is known as _erectile
tissue_, a spongy mass within whose lacunar spaces a large quantity of
blood can, in certain conditions, be retained. When this occurs, the
penis becomes notably thicker and longer, and simultaneously hard and
inflexible. This process is known as _erection_ of the penis, and is
requisite to render possible the introduction of the organ into the
genital canal of the female.

The proximal segment of the urethra is surrounded by the _prostate
gland_. The secretio